The organization of supranuclear pathways involved in horizontal gaze will be studied using axoplasmic transport methods and electrophysiologic techniques. Two specific pathways will be investigated. Oculomotor internuclear neurons have been described lying within the oculomotor nucleus and having terminations in the abducens nucleus and the central tegmental reticular nucleus. Orthograde transport of incorporated radiolabeled amino acids injected into the oculomotor complex will be used to delimit the detail of specific terminations of this important, internuclear projection system. A double retrograde labeling experiment using 3H-wheat germ agglutinin and horseradish peroxidase will be employed to anatomically determine whether individual internuclear cells project to single targets or rather end in both the tegmental reticular nucleus and abducens. In addition, intracellular and extracellular recordings will be made from antidromically identified oculomotor internuclear neurons. Intracellular application of peroxidase will permit direct visualization of individual, electrophysiologically characterized neurons. The combined use of axoplasmic transport methods and intracellular peroxidase injection will provide a strong avenue of approach to the underlying circuitry and organization of the oculomotor internuclear system. A similar approach is proposed for the study of cells in the dorsomedial gigantocellular tegmental field. Cells in this area project directly to the abducens nucleus and may be involved in the generation of rapid eye movements. The projections of this important new brainstem region will be detailed by orthograde transport experiments. Double labeling experiments involving injections of peroxidase and 3wheat germ agglutinin will resolve specific projections of subpopulations within the dorsomedial gigantocellular recticular region. Finally, the intracellular injection of peroxidase into antidromically identified medullary reticular neurons will provide direct visualzation of the location, somatodendritic morphology, and axonal projections of individual dorsomedial medullary reticular neurons. Such experiments will provide critical information regarding the prenuclear assemblies governing eye movement.